Generally, a signal transmitter may mix a data signal with a reference oscillation signal to generate a high frequency output signal. However, when generating the output signal, if the frequency of the output signal is close to the frequency of the reference oscillation signal, these two signals may interfere with each other, which may produce noise to the output signal and lower the quality of communications. To solve this issue, the signal transmitter may further mix the output signal with another reference oscillation signal so that the frequency of the final output signal would be the sum of the frequencies of the two reference oscillation signals, and the output signal will not be interfered by the reference oscillation signals.
However, this approach requires not only extra mixture elements, but also extra filters to reduce the harmonic signals of the output signal. In this case, the circuit area and the power consumption of the signal transmitter would be increased. Therefore, how to reduce the circuit area and the power consumption of the signal transmitter while reducing the noise of the output signal has become an issue to be solved.